1. The Field of the Invention
The present invention pertains to a method and apparatus for transferring liquids between containers and, in particular, to a transfer system which will result in substantially no spillage or adverse environmental effects when the system is disconnected after the transfer is completed.
2. The Prior Art
Transfer of liquids between vessels is a major continuing environmental problem, especially when one considers the large quantities of fluids, many of which may be hazardous, which are transferred on a daily basis. Not only should liquid transfers which occur in the normal routine of commerce be considered in this problem, but also the transfers that are required by industrial emergency situations which seem to arise on an almost daily basis. This would include accidents involving both barges and tank trailers as well as industrial plant accidents in which liquids must be removed from damaged vessels without creating an environmentally damaging situation. Thus it is important to have a spill free liquid transfer system which can have both fixed site embodiments as well as portable, embodiments which could be moved to the site of a required transfer. Either embodiment of the liquid transfer system should have the capability of operating in a hazardous environment, such as in the presence of volatile gases, without causing further potential danger by the use of possible spark generating equipment. Thus the preferred embodiments should rely on either a gas boosted flow or mechanically boosted flow by either a positive displacement pump, a fluid driven pump or a manual pump. The system should also be self purging of all liquid in the transfer lines after the termination of the liquid flow.
It is known to purge liquids from a fluid transfer system using pressurized gas and to force the purged liquids into secondary lines. The following references are representative of this art.
U.S. Pat. No. 5,033,494 to Harbolt et al. discloses a process for the volumetric transfer of liquids comprising the provision a supply 12, transfer tank 20 and drain conduit 36. Of particular interest is the incorporation of a compressed air source 22 and line 40 in such a manner as to purge the transfer tank and conduit of the transfer fluid. The line supplying the pressurized gas is independent of the primary drain conduit 32, but the back end of the gas purging system is conducted through the primary conduit 36, not through a secondary line.
U.S. Pat. No. 5,042,518 to Singhe et al. provides an apparatus and a method for draining fluid from a vacuum line by a drainage pipe having a one way valve permitting the flow of fluids away from the vacuum line and into the tank. A sensor detects a high level of fluid in a tank, thereupon actuating a three way valve to close the vacuum line entry into the tank and simultaneously open a pressurized gas line into the tank to force fluid therefrom. Fluid forced from the tank enters a purge line and a liquid collection line (column 2, lines 12-31)
Of lesser interest, U.S. Pat. No. 5,069,244 to Miyazaki et al. discloses a liquid source container device comprising a main supply 7, gas supply line 18 and delivery (drain) line 19, and several valves on the lines as shown in FIG. 2. The gas is purged from the delivery line by closing valves 20 and 21 and allowing pressurized gas to flow through the delivery line. This system does not entail the use of a secondary, independent line for either admitting gas or receiving residual fluid from a primary line.
Provided solely as background material, U.S. Pat. No. 4,169,225 to Rickert et al. discloses an electric heating apparatus with a system for automatically purging an enclosed volume therein. The actuation method senses low pressure conditions and purging gas is thereupon admitted to the enclosure. The purge gas is not used to force fluids from drainage lines, however.